1. Field of the Invention
The present invention relates to a matrix array drive device for driving a passive matrix array, and a display and an image sensor incorporating such a matrix array drive device.
2. Description of Related Art
In recent years, liquid crystal displays and organic EL (electroluminescence) displays have been widely used as monitors for use in television broadcast receivers, personal computers, mobile telephones and the like due to their advantages such as light weight, slimness and low power consumption.
There are two methods for driving these dot matrix displays. One is an active matrix method in which active elements are disposed at intersections between scanning electrodes (row electrodes) and signal electrodes (column electrodes), and pixels to be lit are selected by the turning on and off of the active elements; the other is a passive matrix method (simple matrix method) in which only pixels are disposed at intersections between scanning electrodes and signal electrodes, and pixels to be lit are directly selected. In particular, most organic EL displays employ the latter method, the passive matrix method, as their drive method.
Examples of a conventional technology related to the foregoing are disclosed in JP-A-2003-280586 and JP-A-2001-265282 (hereinafter called patent document 1 and patent document 2, respectively).
To be sure, in displays employing the passive matrix method, the structure of elements is simple and a high degree of working accuracy is not necessarily required. Thus, it is possible to reduce production cost.
In a conventional passive matrix method, however, N rows of scanning electrodes are scanned one after another, and light is emitted row by row (in other words, vertical scanning is performed line by line), with the result that a period T′ during which one line is selected is 1/N of a unit period T during which one frame is scanned. Thus, as the number N of scanning electrodes is increased, the period T′ during which one line is selected is decreased. Hence, in the case of, for example, an organic EL display, in order to maintain an average brightness required for display, it is necessary to allow each pixel to emit light with N times higher brightness. This places a burden on pixel media and thus causes reduced life and reduced efficiency (for example, reduced quantum efficiency of organic EL elements).
As an example of a conventional technology that overcomes this disadvantage, patent document 1 discloses and proposes a method (so-called double-scan method) in which a screen is divided into two blocks, an upper block and a lower block, and instantaneous current passed through pixels is reduced by driving each block simultaneously.
Disadvantageously, however, for the adoption of such method, a frame memory or the like that latches image data of at least one frame, that is, large circuit overhead is required, and the outputting of image data is delayed by at least one frame, with the result the image data received cannot be displayed in real time.
As an example of a conventional technology that overcomes this disadvantage, patent document 2 discloses and proposes an image display device that has a row drive circuit and a column drive circuit, the row drive circuit having the capability of: simultaneously driving two or more scanning electrodes disposed side by side; continuously producing light emission of light-emitting elements in a horizontal section of scanning electrodes that simultaneously drive light-emitting elements; and thus lighting light-emitting elements one after another, the column drive circuit having the capability of controlling current passed through data electrodes so as to prevent variations in current density of the light-emitting elements.
Disadvantageously, however, in the conventional technology described above, when data for the (N+1)th row is outputted, the reduction of instantaneous current passed through pixels is achieved by selecting not only the (N+1)th row and the Nth row, with the result that an image extends upward and this noticeably reduces vertical resolution.